Mesoscale Discussion 1307
NWS Storm Prediction Center Norman OK
0202 PM CDT Sat Jul 17 2021
Areas affected...Portions of northern VA...DC...central/eastern
MD...eastern PA...DE...NJ...and southern NY
Concerning...Severe Thunderstorm Watch 382...
Valid 171902Z - 172030Z
The severe weather threat for Severe Thunderstorm Watch 382
SUMMARY...The best chance for scattered damaging wind gusts in the
next couple of hours should focus across parts of northern Virginia
into central/eastern Maryland, eastern Pennsylvania, Delaware, New
Jersey, and far southern New York.
DISCUSSION...Storms have started to form into small clusters along
and ahead of a pre-frontal trough across the Mid-Atlantic. The
airmass downstream of these storms is moderately to strongly
unstable, with MLCAPE of 2000-3000 J/kg present. Steep low-level
lapse rates owing to strong diurnal heating of a very well mixed
boundary layer are promoting efficient downdraft accelerations. KEWR
(Newark NJ) measured a peak severe wind gust to 50 kt when a storm
moved through at 1849Z, while KOMH (Orange County Airport in
northern VA) similarly recorded a wind gust to 46 kt at 1815Z.
Modest but sufficient effective bulk shear around 20-30 kt will
likely continue fostering modest storm organization, with multicell
clusters the primary storm mode. Current expectations are for these
clusters to pose a scattered damaging wind threat for the next
couple of hours as they move eastward across northern VA, DC,
central/eastern MD, eastern PA, DE, NJ, and far southern NY,
including the NYC metro area.
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